Method and arrangement for cleaning of a canal

ABSTRACT

The invention relates to a method and an arrangement for the cleaning of a circumferentially closed canal by means of a light guide conducting a laser beam, wherein the entry of the laser beam into the light guide is interrupted when the free end of the light guide is outside of the canal and/or the movement of the light guide within the canal is monitored and if there is no movement or the movement is below a first threshold value then a signal is triggered and/or the laser radiation is turned off or its output is reduced, and wherein the turning off of the laser radiation or its reducing is controlled in dependency of at least one signal change and/or a second threshold and/or a signal change relative to the second threshold determined during at least one course of time starting before and including the entry of the light guide into the canal.

FIELD OF THE INVENTION

The invention relates to a method for the cleaning of acircumferentially closed canal by means of a light guide conducting alaser beam. The invention further relates to an arrangement comprising alaser radiation source, a light guide conducting a laser beam as well asa handpiece.

BACKGROUND OF THE INVENTION

Medical instruments are often in contact with body fluids duringsurgical or diagnostic procedures which always have the risk ofcontamination with bacteria and debris. Many instruments like endoscopesor surgical instruments have small working channels, which are used totransport fluids or e.g. laser fibers into the body of a patient andeven worse body fluids are removed via these channels from the body of apatient.

Therefore, efficient sterilization procedures for those devices areimportant as long the devices are no disposables. Especially the workingchannels are problematic from a hygiene standpoint, as they are not easyaccessible and not visible from outside.

Conventional cleaning is done by soaking in a cleaning fluid and/orflushing a cleaning fluid through the working canals. Typically nodirect check is done whether the cleaning was successful.

SUMMARY OF THE INVENTION

An object of the present invention is it to provide a method and anarrangement for the cleaning of a circumferentially closed canal bymeans of laser beams. In connection with this, it has to be ensured onthe one hand that the canal will not be damaged. On the other hand, itmust also be ensured that persons are not put at risk by the laser beam.Another aspect of the invention is it to provide the possibility thatthe cleaning of the canal can be carried out in a simple manner whereinthe procedure helps avoiding errors. Another aspect of the invention isto provide a compact unit by means of which the treatment as cleaningwill be carried out.

The arrangement shall, in particular, enable its use without risking anincorrect treatment. It shall provide the possibility of an automatedcanal cleaning and canal treatment.

To solve one or more aspects, the invention provides a method for thecleaning of a circumferentially closed canal by means of a light guideconducting a laser beam, wherein the entry of the laser beam into thelight guide is interrupted when the free end of the light guide isoutside of the canal and/or the movement of the light guide within thecanal is monitored and if there is no movement or the movement is belowa first threshold value then a signal is triggered and/or the laserradiation is turned off or its output is reduced, and wherein theturning off of the laser radiation or its reducing is controlled independency of at least one signal change and/or a second thresholdand/or a signal change relative to the second threshold determinedduring at least one course of time starting before and including theentry of the light guide into the canal.

According to a further independent proposal it is provided that theturning off of the laser radiation or its reducing is controlled independency of at least two signal changes and/or two second thresholdsdifferent from each other and/or signal changes relative to the twosecond thresholds determined during at least two courses of timestarting before and including the entry of the light guide into thecanal.

An independent proposal to solve the problem provides that the positionof the free end of the light guide within the canal is checked and/ormonitored.

According to a further independent proposal it is provided that amaterial present on the inside of the canal is removed throughlaser-induced hydrodynamic fluid movement.

According to a further independent proposal it is provided that aclosure element is secured to one free end of a light guide conducting alaser beam, the light guide with the closure element is introduced intothe canal, that the closure element is positioned in the region of thecanal to be sealed and after positioning of the closure element energyis introduced, the closure element melts and/or softens and remains inthis position in the canal and seals it tightly.

According to a further independent proposal it is provided that theclosure element is melted through the laser radiation transmittedthrough the light guide or through electrical energy.

According to a further independent proposal it is provided that theclosure element is connected to the free end of the light guide by meansof a connecting material, with the melting temperature T1 thereof beinghigher than the melting temperature T2 of the closure element material.

According to a further independent proposal it is provided that aftersealing of the canal, in particular its opening, a closure material isintroduced into the canal and the light guide within the closurematerial is moved in the longitudinal axis direction of the canal at thesame time as the laser beam is introduced.

According to a further independent proposal it is provided thatmechanical effect of the energy introduced into the closure material viathe laser radiation is greater than the macroscopic thermal effect ofthe energy introduced.

According to a further independent proposal it is provided that asealing material is used that melts and/or foams through theintroduction of heat energy and forms a closed-pore canal seal aftercooling, in particular that sodium hydrogen carbonate enveloped by guttapercha material is used as the sealing material.

According to a further independent proposal it is provided that amaterial that comprises a first component and a second component whichreact with one another in a volume-expanding manner is used as sealingmaterial.

According to a further independent proposal it is provided that amaterial is used as a closure element that comprises an in particularvolume-scattering core material and an expanding material that envelopsit.

According to a further independent proposal it is provided that anEr:YAG laser, Er:YSGG laser or CTE laser is used as the laser.

According to a further independent proposal it is provided that thelaser is operated with a pulse duration between 5 μs and 1000 μs,preferably between 25 μs and 400 μs, and especially preferably between50 μs and 200 μs.

According to a further proposal it is provided that a laser beam is usedthat has a pulse energy exiting from the light guide between 0.5 mJ and50 mJ, in particular between 1 mJ and 10 mJ.

According to a further independent proposal it is provided that averification of whether the light guide is inside the canal or outsidethe canal is carried out through

-   -   a) the radiation received by the light guide that is derived        from the area surrounding the light guide, and/or    -   b) through the changing reflection component of the radiation        reflected at the end of the light guide, and/or    -   c) measurement of a change in impedance via an outer        metallization of the light guide, and/or    -   d) measuring the distance to the nearest object in the vicinity        of the fiber tip with time of flight measurement (TOF), and/or    -   e) measuring the ambient light with a sensor integrated in the        TOF chips, and/or    -   f) measuring the distance to the nearest object in the vicinity        of the fiber tip by ultrasound pulses.

According to a further independent proposal it is provided thepositioning of the light guide is verified redundantly by anycombination or selection of options a) to f), in particular by means ofthe steps a)+b) or a)+c) or b)+c) or c)+f), especially preferred bymeans of a)+b)+c) or c)+d) or d)+e) or c)+d)+e).

Subject matter of the invention is also an arrangement comprising alaser radiation source arranged within a laser device, a light guideconducting a laser beam as well as a handpiece, wherein the handpiece isdetachably connected, preferably rotationally, to a delivery device, viawhich at least the laser beam and a liquid can be fed to the handpiece,as well as a first line guiding the liquid, that extends with itsaperture side in the region of the light guide, and with the laser beambeing directed into a canal via the light guide detachably connectedwith the handpiece, wherein at least on pre-pressurized fluid containeris attached to the laser device.

A further proposal according to the invention provides that thehandpiece is connected to at least one cleaning fluid container or hassuch a container, from which a line emanates, the opening of whichextends on the light guide side.

A further proposal according to the invention provides that the cleaningfluid container is connected to the handpiece such that it can bedetached or plugged on to it.

A further proposal according to the invention provides that the devicehas further exchangeable, disposable containers for different cleaningfluids (as sterile water and/or NaOCl and/or EDTA and/or PDT-fluids)which are pressurized by compressed air of a dental chair provided by adental turbine connector.

A further proposal according to the invention provides that the cleaningfluid container is provided with a closable exit opening that can becontrolled by an electromagnetically-actuatable valve controlled by amicrocontroller.

A further proposal according to the invention provides that theelectromagnetic valve is separated into an excitation part with amagnetic coil and a part of a ferromagnetic core in the hand piece and aferromagnetic material as valve opener as part of the exit valve in acontainer.

A further proposal according to the invention provides that a flexiblemembrane or a piston separates the fluid from an air inlet.

A further proposal according to the invention provides that at least onefluid container is attached to the laser device and the laser device hasno connection to a dental chair/dental treatment center and no air isneeded to generate the water mist exiting the hand piece.

A further proposal according to the invention provides that the lightguide has a metallisation on its outer surface.

A further proposal according to the invention provides that the lightguide has a metallisation on its outer surface with two regions that areelectrically insulated with respect to one another.

A further proposal according to the invention provides that the regionsinsulated with respect to one another enmesh in one another in acomb-like manner at least at the tip of the light guide.

A further proposal according to the invention provides that themetallisation has hydrophobic characteristics over at least the anterior⅓ of the light guide.

A further proposal according to the invention provides that a movementsensor is integrated into the handpiece.

A further proposal according to the invention provides that a movementsensor and a rotation encoder are integrated into the handpiece forrecognition of the handpiece rotation with respect to a delivery system.

A further proposal according to the invention provides that the lightguide between a delivery device and the handpiece is made of a material,in particular of GeO, sapphire or ZrF₄, which conducts laser pulses upto 50 mJ and/or a mean laser output of 5 W in the wavelength rangepreferably between 2.69 μm and 2.94 μm, as well as in particularadditionally in the wavelength range between 400 nm and 1000 nm.

A further proposal according to the invention provides that the lightguide to be introduced into the canal is made of a material, inparticular of OH-reduced silica or sapphire, which conducts laser pulsesup to 50 mJ and/or a mean laser output of 5 W in the wavelength rangepreferably between 2.69 μm and 2.94 μm, as well as in particularadditionally in the wavelength range between 400 nm and 1000 nm.

A further proposal according to the invention provides that the diameterof the light-conducting core of the light guide lies between 150 μm and600 μm, in particular between 118 μm and 250 μm, wherein the light guidepreferably has a protective layer on its outer side.

A further proposal according to the invention provides that the lightguide has an outer diameter between 200 μm and 300 μm and/or a lengthbetween 25 mm and 40 mm.

A further proposal according to the invention provides that the laser isa diode-pumped Er:YAG laser, Er:YSGG laser or CTE laser with, inparticular, a pulse duration between 5 μs and 1000 μs, preferably in therange 25 μs to 400 μs, especially preferred 50 μs to 200 μs, and/or apulse energy between 0.5 mJ and 50 mJ, in particular between 1 mJ and 10mJ and/or a mean output between 0.5 W and 10 W, preferably between 1 Wand 3 W, with a pulse repetition rate in the range 50 Hz to 2000 Hz,preferably 50 Hz to 800 Hz.

A further proposal according to the invention provides that thearrangement is provided with a control device, as well as a housing thatencloses the laser, which is connected to a supply device, in particulara medical one, through which the arrangement can be supplied with waterand/or compressed air.

A further proposal according to the invention provides that the controldevice is provided with a touchscreen.

A further proposal provides that the laser device is a table top deviceenclosing the laser source, and is not connected to a supply device andhas its own pre-pressurized fluid container attached.

Using a laser to generate steam bubbles and generating rapid fluidmotion can improve the cleaning of small instrument canalssignificantly. Of course it is important not to damage the inner surfaceof the canals, which are often made of polymers and plastics. Thereforea laser with low pulse energy below the ablation threshold of the canalwall material is required. A diode pumped Er:YAG laser is ideal for thispurpose, since the pulse repetition rate can be much higher than withconventional flashlamp pumped laser systems and can compensate for alower pulse energy per pulse.

Killing bacteria in the working canals can be enhanced by usingtransient heat pulses as described in the text above Low power Er:YAGlaser radiation in the order of 0.5 W with 200-800 Hz pulse repetitionrate is fully sufficient to reach transient local peak temperatures onthe canal wall well above 100° C. for killing bacteria and keeping thebase temperature of canal wall material well below melting point ordestruction thresholds.

It is important not to stay in one position with the cleaning fiberbecause this could cause local overheating of the sensitive canal walls.Therefore the motion detection of the fiber is an additional safetyfeature in this cleaning application.

For laser safety reasons it is further helpful to avoid laser emissionbefore the cleaning fiber is introduced into the canal. Therefore a“fiber in canal detection” is provided with details described elsewherein this text.

Additionally PDT (photodynamic therapy) protocols can be applied usingfluids like Methylen Blue or Toluidin Blue, which are applied into thecanal and the appropriate light is coupled into the light passing downinto the canal. For Methylen Blue 670 nm with around 150 mW are requiredand 635 nm with ˜100 mW for Toluidin Blue. The advantage overtraditional PDT procedures is the simultaneous delivery ofEr:YAG/Er:YSGG laser energy to agitate the PDT fluid by laser energy,rapidly induce steam bubbles, adjacent fluid motion and heat the PDTfluid. This allows a much more intense contact of the fluids with thebacteria and debris.

Further it is helpful to know whether the cleaning procedure wassuccessful by detecting remaining bacteria in the canals as described inthis text with the example of root canal cleaning.

Of course this is not the only application for this cleaning technology.Many biotechnology procedures/bioreactors are endangered by bacteria,algae and debris deposition in small canals which can be cleaned withthe proposed procedure and device.

And of course larger canals exceeding 1 mm diameter can be cleaned withthis procedure as well then however requiring more laser pulse energyand multiple cleaning fibers positioned e.g. in an array or ringstructure Required pulse energies are then in the order of n*0.1-50 mJ,where n is the number of single cleaning fibers.

In case of cleaning longer canals the terminal fiber introduced in thecanal must have a better transmission than OH reduced silica. In thatcase sapphire is the ideal candidate material.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be better understood and its advantagesappreciated by those skilled in the art by referencing to theaccompanying drawings. Although the drawings illustrate certain detailsof certain embodiments, the invention disclosed herein is not limited toonly the embodiments so illustrated.

FIG. 1 depicts a diagram of a light guide with removable plug,

FIG. 2 depicts a diagram of a light guide inserted into a canal with anexpanding plug,

FIG. 3 depicts the arrangement according to FIG. 2 with an expandedplug,

FIG. 4 depicts a diagram of the arrangement according to the invention,

FIG. 5 depicts a diagram of an electrode arrangement of the light guidetip,

FIG. 6 depicts a block diagram of a laser system,

FIG. 7 depicts a block diagram of the delivery system,

FIG. 8 depicts a diagram of a handpiece,

FIG. 9 depicts a schematic diagram of a handpiece,

FIG. 10 depicts a diagram of a handpiece with fluid cartridges,

FIG. 11 depicts a diagram of a cartridge with valve,

FIG. 12 depicts a diagram of a light guide,

FIG. 13 depicts a hand piece with fiber tip and TOF detection

FIG. 14 depicts details of the TOF detection

FIG. 15 depicts time diagrams of the various options of “fiber in-canaldetection” for root canal treatment

FIG. 16 depicts time diagrams of the various options of “fiber in-canaldetection” for non-medical applications

FIG. 17 depicts time diagrams of the various options of “fiber in-canaldetection” for abuse of the device.

FIG. 18 depicts the placement of the cleaning fluid container on thelaser system

FIG. 19 depicts details of the cleaning fluid container

DETAILED DESCRIPTION OF THE INVENTION

In the following, the invention will be explained on the basis of thecleaning of a canal, such canal being a root canal, however, withoutlimiting the invention. Rather, the teaching according to the inventioncan be applied in all cases where particularly canals with smalldiameters are to be cleaned and/or closed as is for example the casewith medical instruments, as explained in the introduction.

In case of a traditional root canal treatment, the pulp chamber isopened, the pulp tissue removed and the root canals are enlarged withmechanical files until a conical shape of the root canal is achieved.The canal is manually flushed with cleaning fluids via syringes. Thenthe canal is filled with a sealer and conical gutta-percha points areplugged and condensed into the canal to achieve a dense root canalfilling.

For this procedure canal enlargement is necessary to create a conicalshape of the canal consistent with the conical shape of the Gutta-perchapoints filling the canal. The material loss weakens the tooth; theprocedure is time consuming, bears the danger of over-instrumentationand file fracture. The success rate ranges from below 70% to 95%depending on who is doing the treatment.

An easier, less time consuming and technique sensitive procedure couldhelp to raise the average success rate and increase the comfort for thepatient.

A procedure without enlarging the root canal would avoid above mentioneddisadvantages. However it creates new challenges. Not enlarging thecanal results in irregular shaped root canals like a cave. Thereforetraditional root canal cleaning and filling is not possible, becauseconically shaped Guttapercha points cannot be inserted in such anunshaped root canal. A new filling technology is required.

Laser assisted root canal procedures use steam bubbles generated bylaser energy to cleanse root canals which are already enlarged withmechanical files to a conical shape typically to size #40 or more. Thesteam bubble expansion and contraction causes water motion in thevicinity of the bubbles, which then cleanse the root canal walls.

Fotona, Biolase and KaVo sell or have sold dental laser systems whichcan be used for such an endodontic treatment. These lasers offer a widerange of dental indications up to drilling of cavities. The pulserepetition rate of these devices is typically limited to ˜50 Hz and theyoffer pulse energies up to 1 J, which is necessary for cavitypreparation. For endodontic treatment pulse energy below 50 mJ issufficient in combination with 50 Hz or pulse repetition rate (Thermaland acoustic problems on root canal treatment with different lasers, T.Ertl, H. Benthin, G. Müller, SPIE Vol. 2327 Medical Applications ofLasers 11(1994); Application of lasers in endodontics, T. Ertl, H.Benthin, B. Majaron, G. Müller, SPIE Vol 3192 Medical Applications ofLasers in Dermatology, Ophtalmology, Dentistry and Endoscopy (1997)) andthe use of conical shape fiber tips (Canal Enlargement by Er:YAG LaserUsing a Cone-Shaped Irradiation Tip, S. Shoji, H. Hariu, H. Horiuchi, JENDONTICS VOL. 26, No. 8. August 2000; 454-458).

These traditional flash lamp pumped Er:YAG/YSGG laser have an energyconversion efficiency of ˜3% resulting in a large power supply and abulky device with fluid cooling. This leads to a high price and thusvery limited number of users.

Additionally these lasers are class 4 devices, the regulatoryenvironment needs some efforts in a dental practice to comply with. Alaser safety area must be declared and protected, a laser safety officermust be trained and nominated and DDS, assistant and patient need towear eye protection goggles.

The actual laser assisted endodontic root canal procedure uses pulseenergies in the range 5-30 mJ pulse energy, which is above the ablationthreshold of dentin. Therefore generating a wrong pathway (via falsa) ispossible, when protruding the laser fiber into the root canal.

In a protocol provided by DiVito (Effectiveness of the Erbium: YAG laserand new design radial and stripped tips in removing the smear layerafter root canal instrumentation, E. DiVito, O. A. Peters, G. Olivi,Lasers Med Sci (2012) 27:273-280) the laser applicator is placed in thepulp chamber and not protruded into the root canals. Even without theneed for protruding the laser applicator into the root canal theprocedure requires pretreatment of the root canals to size #25 or #30.The laser energy generates fluid movement in the pulp chamber, whichextends into the root canals partially. In favor of the method no fibermust be protruded into the canal. However disadvantages are inconsistentresults, depending on the canal geometry and splashing of corrosivecleaning fluids out of the pulp chamber even out of the mouth of thepatient can be observed due to relative high pulse energies of 25-30 mJ.

Recent technology improvement enabled the design of diode pumpedEr:YAG/YSGG lasers.

A diode pumped Er:YAG/Er:YSGG laser developed specifically forendodontic treatment offers a smaller device and more economicalsolution. This laser system is based on laser system developed byPantec. (WO 2010/145802 A1, Bragangna, Heinrich, Pantec Biosolutions AG)Main reason is an improved efficiency of the conversion of electricalenergy into light energy. This allows using a much smaller power supplyand reducing the cooling efforts.

A higher pulse repetition rate (up to 2000 Hz compared to 50 Hz) allowsdecreasing the pulse energy below the ablation threshold of dentin. Thisis important, because it avoids the formation of a “via falsa”(penetrating the root canal wall into the periodontium), which is asignificant complication in endodontic treatment.

Totally unexpected, pulse energies in the range of 0.8-4 mJ incombination with pulse repetition rates between 50 Hz and 2000 Hzpreferably 50 Hz-800 Hz allow in combination with effective cleaningfluids efficient cleaning of root canals. The low pulse energy avoidssplashing of the cleaning fluids, minimizes the vibration of the toothduring treatment and avoids a root canal wall perforation by the laserfiber during treatment, because the laser energy density is below theablation threshold of dentin.

The canal treatment as a root canal treatment with the device disclosedaccording to the invention starts like the traditional procedure withopening the pulp chamber, removing the pulp tissue in the pulp chamber,searching for the canal entrances and slightly enlarging the entrances,followed by path finding with file size up to size #25 which created apathway with at least 250 μm diameter at the apex and more diameter morecoronal, which is necessary to protrude a laser fiber with same orsmaller diameter close to the apex.

No further canal enlargement is required. This saves significant workingtime and increases the patient comfort

The pulp chamber and the root canals are filled with cleaning fluideither manually with a syringe or automatically from fluid containers ofthe device and the laser fiber is inserted in to the root canal until 1mm before the apex.

The laser radiation in a wavelength range 2.69-2.94 μm is stronglyabsorbed by fluids containing water and creates steam bubbles byvaporization in the fluid and causes hydrodynamic motion of the water inthe root canal. This fluid motion cleanses the canal. The laser isactivated and the laser fiber is moved up and down the root canal.Cleaning consists of removing vital and non-vital pulp tissue, bacteriaand pus as well as opening the dentinal tubules. The main cleaning areais ˜1-2 mm around the fiber tip and some less efficient “far distance”cleaning effects in the whole root canal, mainly caused by resonancephenomena as interaction between the root canal geometry and acousticwaves caused by steam bubble formation and collapse.

After cleaning, the canal with one fluid the canal is dried eitherconventionally with paper points or with laser energy (or both combined)to remove the cleaning fluid from the canal. Additionally compressed aircan be used exiting the applicator supporting the drying process. Thenoptionally further cleaning fluids are filled into the root canalssequentially (Manually with syringes or automatically with the device)and the treatment is repeated. Finally the canal is dried again.

Possible cleaning fluids can be water, comprising NaOCl (3-10%), EDTA(10-17%), and H₂O₂ (3-30%) or mixtures thereof.

Verdaasdonk et al. (WO 2013/049832 A2, Biolase inc., Netchitailo V.,Boutoussov, D. Verdaasdonk, R. M. et al. Pressure wave root canalcleaning system) report on cleaning improvement with laser energies,typically larger than 5 mJ per pulse by adding gas bubbles to thecleaning fluid.

In contrary to Verdaasdonk's, disclosure cleaning with low pulseenergies in the proposed range is less efficient, if the fluid containsgas bubbles before treatment. Best results are obtained with fluidswithout addition of gas bubbles or even degassed fluids.

To decide, whether a root canal is clean and dry enough and free ofbacteria, a cleanliness check of the root canal can be done.Spectroscopic/fluorescent methods can be used guidingillumination/excitation light in the laser fiber into the root canal andcollecting remitted light from the bacteria, debris and canal wall withsame fiber. This can be done simultaneously to the laser cleaning.Bacteria emit fluorescence signatures in the visible wavelength range(especially 570 nm-650 nm) when excited with UV light (e.g. 405 nm) orin the near infrared range (e.g. 750-880 nm), when excited with redlight 600-700 nm. Excitation in the visible range is preferable, becauseauto-fluorescence of dentin has a strong emission in the green spectralarea around 530 nm.

Alternatively electrical impedance spectroscopy can be applied for canaldiagnostics.

In case bacteria remain after cleaning in the root canal bacteria can bereduced by a specific temperature treatment using high repetition ratelaser energy or/and a PDT procedure can be added to the treatment.

A pre-requisite for thermal killing of bacteria is a strong absorptionof the laser radiation at the root canal surface. Diode lasers withemission wavelength between 750 nm and 980 nm used today for thispurpose do not have a strong absorption in dentin, therefore are notideal in part even dangerous, since the temperature rise in theperiodontium and inside the root canal are nearly equal.

2.69-2.94 μm wavelength e.g. of the proposed diode pumped Er:YAG laserdevice is much better adapted to the task.

Therefore, low power Er:YAG laser radiation in the order of 0.5 W with200-800 Hz pulse repetition rate is fully sufficient to reach local peaktemperatures on the root canal wall well above 100° C. for killingbacteria and keeping the periodontal temperatures well below critical43° C.

For PDT various protocols are available (e.g. Helbo, Dentofex, Wilson).For this treatment fluids like Methylen Blue or Toluidin Blue areapplied into the root canal and the appropriate light is coupled intothe light pass down into the root canal. For Methylen Blue 670 nm witharound 150 mW are required and 635 nm with ˜100 mW for Toluidin Blue.The advantage over traditional PDT procedures is the simultaneousdelivery of Er:YAG/Er:YSGG laser energy to agitate the PDT fluid bylaser energy, rapidly inducing steam bubbles, causing adjacent fluidmotion, and heating the PDT fluid. This allows a much more intensecontact of the fluids with the bacteria and increases the penetrationdepth into the dentinal tubules compared to PDT without agitation oragitation with ultrasound.

Filling not enlarged canals 10 as root canals requires a new approachcapable of covering irregular root canal space without voids. This ispossible with a low viscosity obturation material. The risk is however apenetration of the filling material over the apex.

An apical “plug” placed in the apical region before filling the canalwith the low viscosity material can prevent this. Conventional solutionsfor placing an apical plug are disclosed already (e.g. US2009/0220909 A1Müller, Mannschedel, Coltene/Whaledent) but require however a canalpreparation according to ISO and cannot be applied to irregular canals.Further they do not disclose the use of a laser system to place theplug.

In case of a small apex with a diameter in the order of laser fiber(250-350 μm) a plug 12 is attached axially to the laser fiber 14 (FIG. 1). Optional a connection material 16 between the fiber tip 18 and theplug 12 may improve the adhesion between plug material and the fiber tip18.

The plug material may be pre-heated before insertion in an externalfurnace actually used to pre-heat Thermafil obturators.

The plug material may be covered additionally with a sealer prior toinsertion in the root canal 10. The sealer may be composed as disclosedin US2014/0017636 A1 Berger et al., Dentsply intl. inc.

The laser fiber 14 with the plug 12 is protruded in the root canal 10and pushed with slight pressure in position. At appropriate workinglength (length to apex—1 mm) the laser is activated and the plug 12 orthe connection material 16 begins to melt at the connection to the laserfiber 14. The plug 12 can be slightly vertically condensed with thelaser fiber 14. That will hold the plug 12 in position while removingthe laser fiber 14. In the next step the low viscosity material isfilled into the canal. This material can be e.g. a root canal fillingmaterial as disclosed in US 2014/0335475 A1 Berger el al., Dentsplyintl. inc.

To improve the coverage of the root canal wall in recesses and notdirectly accessible areas the low viscosity filling material can besubjected to laser radiation, which is absorbed by the material andcreate steam bubbles, which accelerate the material against the rootcanal wall. Finally a material with same or higher viscosity (e.g.according to US 2014/0335475 A1) is filled into the canal to obturatethe remaining canal volume. Lateral and/or vertical condensation may beapplied.

Requirements for the plug material:

-   -   Bio-compatible    -   Hardness lower than dentin (relevant in case of re-treatment),        gutta-percha is an option.

In case of a direct connection of the gutta-percha to the laser fiber 14the gutta-percha formulation must have a stable connection to the laserfiber 14 at storage and during insertion into the canal 10 at roomtemperatures and must melt in between 50° C. and 200° C. Gutta-perchahas an absorption coefficient high enough to deposit enough energy in afew 10^(th) of micrometers, which ensures a very local heating of theinterface to the laser fiber.

In case a connection material is used the connection material 16 mustmelt in between 45° C. and 200° C. and attach sufficiently to the laserfiber 14 and the plug material. The absorption coefficient at the laserwavelength must be high enough to deposit sufficient energy in a few10^(th) of micrometers to melt the connection material with a power ofless than 2 W, preferably below 100 mW within 1-3 seconds. The materialmelts between 45° C. and 200° C., which insures shelf stability andkeeps the temperatures in the apical region low enough during the heatapplication.

Alternatively the gutta-percha plug may be attached to an applicatorwhich is heated electrically. A tiny SMD resistors (EIA01005,0.2×0.2×0.4 mm) or semiconductor material at the tip of a plasticapplicator feeded by 2 copper wires with less than 250 μm total diametercan be used.

In case of a wide apex 20 much wider than the fiber diameter e.g. 0.5-1mm the above described approach would fail.

For such a situation a material is needed that can expand the volume “ondemand” (like popcorn or polyurethane foam). The base material could beattached again to the laser fiber 14 protruded in position at the apex20 and then the expansion is initiated by either laser energy convertedto heat by absorption or UV light, but with a plug 112 comprising anexpandable material 114. The plug material 114 must expand attemperatures lower than the melting temperature of the connectionmaterial. After expansion of the plug material 114 and after some secondof cooling to allow the plug material 114 to get harder, the laser poweris increased for a short time duration e.g. 0.5-2 seconds to finallymelt the connection material and remove the fiber tip 14 from the canal10 without the danger of displacing the plug 112 from its apicalposition during removal.

Ideally the expansion of the plug material 114 is directed towards thecanal wall. To achieve this, the expandable material must be placed onthe side of a volume scattering material attached to the fiber tip 18with a connection material. After expansion this volume scatteringmaterial 114 will remain in the canal 16 as part of the plug 112. Toseparate the plug from the fiber tip, the connection material is heatedwith Er:YAG laser radiation. In this case the connection material mustbe transparent for radiation in the visible range, which is scattered byvolume scattering part 120 of the plug 112 into the expandable plugmaterial 114 to heat the expandable plug material 114.

The plug material can be a dental composite material. The connectionmaterial can be a translucent (in the visible wavelength range) resinsoftening at less than 200° C.

The plug 112 with the middle part of the scattering material 120 and theexpandable material 114 surrounding the core is depicted in FIGS. 2 and3 .

Another option is attaching a material component A as expandable plugmaterial to the laser fiber and a second Material B is applied to thefirst material just before insertion into the root canal, which starts areaction with volume expansion. The laser energy would then only be usedto melt the connection of the plug material and the laser fiber, whichhas kept the plug material in the correct position before it fixesitself to root canal wall by expansion.

A material with an expansion factor of 3 can fill the gap between a #25(250 μm diameter) plug and an apex diameter of #40 (400 μm diameter). Anexpansion factor of 7 can fill the gap to an apex diameter of #60 (600μm).

In case a fiber tip with larger diameter can be inserted without canalenlargement, which is often the case in anterior teeth a material withan expansion factor of 3 could fill the gap between a #40 (400 μmdiameter) plug and an apex diameter of #70 (700 μm diameter). Anexpansion factor of 7 could fill the gap in this example to an apexdiameter of #100 (1000 μm).

Example for an expandable material: A mix of Natriumhydrogencarbonat(sodium bicarbonate)+guttapercha particles. When heat is applied via theoptical fiber tip the following reaction 2 NaHCO₃→Na₂CO₃+CO₂↑−H₂Oreleases CO₂ and forms a foam with the meltede Guttapercha particles.

To keep the pH in physiological range an acid (e.g. Citric acid) may beadded which will produce additional foam in a moist environmentAlternatively any biocompatible foaming agent in combination withGuttapercha including the disclosure in US2014/0017636 A1 and US2014/0335475 A1 both Berger et al., Dentsply intl. inc. can be used.

Small sodium bicarbonate particles may be encapsulated in gutta-perchato create a closed bubble foam.

Examples of different kind of plugs, plug materials, connectionmaterials, and expandable materials are specified in Table I.

TABLE I Connection material Plug Options Plug material (Plug to fiber)Expandable material Option 1 Guttapercha, Thermafil (Plug materialdirectly fixed to fiber tip, no expansion) Option 2 Guttapercha,Thermafil “Glue” melts (Plug material glued between 50 and 200° C., withconnection material biocompatible good to fiber tip, no expansion)adhesion to silica fiber and guttapercha Option 3 .=expandable material“Glue” melts biocompatible material expands (Expandable plug materialbetween 80° C. and 200° C., 3 to 7 times the original volume glued withconnection biocompatible good Expansion may start by heat material tofiber tip adhesion to silica (Temperature 50-70° C.) fiber andguttapercha must be flexible like guttapercha Option 4 Plug basematerial Optical Glue melts between biocompatible material expands(volume scattering plug base properties like a Dental 80° C. and 200°C., 3 to 7 times the original volume material glued with connectioncomposite “Transpa” or biocompatible good Expansion may start by heatmaterial to fiber tip, and “Enamel” semitranslucent adhesion to silicafiber (Temperature 50-70° C.) covered with expandable material and sidescattering >60% and guttapercha must be flexible like guttapercha on thecone walls and apical) in visible spectral range must be flexible likeguttapercha biocompatible

A device according to the invention is shown in principle in FIG. 4 .The device comprises a desktop device 40 with a touch screen 42 and ahousing with integrated cooling elements 44.

The housing is connected to the turbine connector of a dental unit 6(connector 46) to have supply with water and compressed air.

The desktop housing is connected to a handpiece 48 with a deliverysystem 50.

The handpiece 48 is connected to the delivery system 50 via a rotationcoupling. A fiber tip 52 can be connected to the handpiece anddisposable containers 54 with cleaning fluid can be attached and removedfrom the handpiece. The housing is connected with the handpiece 48 via aconnecting line 56.

The portable desktop device 40 comprises a laser as energy source. Thelaser radiation is transmitted with a delivery system together withwater and compressed air and optionally cleaning fluids to the handpiece48 with detachable fiber tip 52.

The energy source is a Diode pumped ER:YAG—(Wavelength 2.94 μm),Er:YSGG—(Wavelength 2.78 μm) or CTE Laser (wavelength 2.69 μm). Thepulse length is between 5-1000 μs, preferably 25-400 μs, most preferably50-200 μs. The pulse energy is between 0.5-50 mJ, preferably 1-10 mJ atthe distal end of the applicator. This requires around the double pulseenergy at cavity exit. The average power is between 0.5-10 W preferably1-3 W and the peak power is <600 W at cavity exit.

Further the device is equipped with light sources for aiming beam andapical plug heating and optional for bacteria detection and for PDT.

The aiming beam is coupled through the Er:YAG rod from the 100%reflection mirror side and the other light source for apical plugheating and PDT is coupled into the light path with a dichroitic beamcombiner. High power LEDs or laser diodes e.g. ADL-63V0ANP (LaserComponents) may be used. The laser diode may be operated in parallel tothe MID IR laser and is simultaneously transmitted to the handpiece. Forfluorescence excitation (bacteria detection, canal cleanlinessdetection) cw or pulsed laser diodes in the range 350-700 nm are used.

The device uses preferably air cooling for laser cavity and electronics.

A schematic depiction of the laser system is shown in FIG. 6 which isself-explaining.

Especially, the invention is characterized by a diode pumpedEr:YAG-/Er:YSGG/CTE:YAG laser providing a cleanliness check of the canalas root canal via the same optical fiber used for the canal cleaningwith the following excitation/detection wavelength ranges for bacteriafluorescence detection.

-   -   a) Excitation 405-450 nm/detection 570-650 nm    -   b) Excitation 600-700 nm/detection 750-880 nm.

Further, the invention is characterized by a diode pumpedEr:YAG-/Er:YSGG/CTE:YAG laser providing a cleanliness check of the canalas root canal via a metallization layer on the optical fiber tip usedfor the root canal cleaning using electrical impedance spectroscopy.

In addition, the invention is characterized by a diode pumpedEr:YAG-/Er:YSGG/CTE:YAG laser providing energy (0.05 W-3 W with 200-800Hz pulse repetition rate) into the canal as root canal via a fiber optictip to heat the root canal inner surface via radiation absorption up toa 500 μm vicinity to temperatures lethal for bacteria reaching localpeak temperatures on the root canal wall well above 100° C. and keepingthe periodontal temperatures well below critical 43° C.

A further feature of the invention is a diode pumpedEr:YAG-/Er:YSGG/CTE:YAG laser providing an additional light sourceemitting at 670 nm with around 80-200 mW and/or 635 nm with 50-150 mW tosimultaneously initiate PDT with fluids like Methylen Blue or ToluidinBlue and agitate the PDT fluid by laser energy with rapidly inducedsteam bubbles and adjacent fluid motion and heat.

Water and compressed air are provided by plugging a dental turbineconnector in a socket of the device. The device may have furtherexchangeable containers 54 for different cleaning fluids (sterile water,NaOCl, EDTA), if these containers 54 are not positioned directly at thehandpiece 48. These cleaning fluid containers are pressurized by thecompressed air of the dental chair provided by the dental turbineconnector 46.

The fluid flow from these containers 54 to the handpiece 48 iscontrolled with electromagnetic valves operated via the μC (embeddedmicro-controller). Controlling the laser parameters and the sequencingof the cleaning fluids, laser assisted drying and compressed air allowsa fully automated cleaning process canal by canal (TABLE II). Thedentist needs just to press a start button and then move gently thefiber in the canal up and down until a ready sign appears (LED or Beep).Then the fiber 14 is inserted in the next canal and the procedure isrepeated.

TABLE II 30 s Optional: H₂O, 100 Hz, 1.8 mJ (Pre - cleaning) with lowAVG power, create access for water in deeper canal sections) 30 s H₂O,400 Hz, 1.8 mJ (Cleansing with 0.8 W AVG power) 10 s Rinse & dry canalswith laser 800 Hz, 0.5 mJ, (laser drying is faster than with paperpoints) 30 s 5.2% NaOCl 400 Hz, 1.8 mJ (Dissolve pulp tissue) 10 s Rinse& dry canals with laser 800 Hz, 0.5 mJ 60 s 17% EDTA 50 Hz, 3.5 mJ(every 6 s for 1 s laser treatment) 10 s Rinse & dry canals with laser800 Hz, 0.5 mJ

Parameter Range

Min-Max

[Preferred Min-Max]

TABLE III g Time [s] Pulse energy [mJ] Pulse repetition rate [Hz]Pre-cleaning 10-120, 0.25-30 50-500 [20-60]  [0.5-10] [50-200] Cleaning10-120, 0.25-60  50-1000 [20-60]  [0.5-20] [50-400] Drying 5-30, 0.25-5 100-2000 [5-15] [0.25-2]  [200-1000] Cleaning 10-120, 0.25-60  50-1000with NaOCl [20-60]  [0.5-20] [50-400] Cleaning 10-120, 0.25-60  50-1000with EDTA [20-60]  [0.5-20] [50-400]

The laser parameters used when cleaning a canal are specified in TABLEIII.

Mechanisms are provided to ensure that the laser can only operate, ifthe laser fiber 14 is placed in the root canal 10 to reduce laser safetyrisks.

When the fiber tip 18 is inserted into the root canal 10 the lightreceived through the fiber 14 is far less compared to the fiber 14 beingin ambient light. A detector in the laser system measures the lightcoming back from the fiber tip 18 and detects the absolute light leveland the change in light level (first derivative). This detection can bedone independently from any micro-controller or detection software. Itis based on fixed wired hardware with a fail-safe design, which disablesthe laser system in case of a hardware fault in the detection unit.

The electronics further can detect the change of reflection of lightemitted into the fiber delivery system (e.g. the aiming beam) when therefraction index difference changes while immersing the fiber tip 18into the fluid contained in the root canal. The light of the aiming beamis amplitude modulated to differentiate the signal from the ambientlight.

FIG. 13 shows another method for the “fiber in canal detection”. Thismethod performs a distance measurement between a front of an applicationhand piece 212 and an entrance 214 of a canal 216, which is surroundedby solid material/tissue.

When a fiber tip 218 enters the canal 216 the distance D between thematerial surrounding the canal entrance 214 begins to get smaller thanthe fiber tip length L, which can be used as an indicator that the fibertip 218 has entered a canal.

Technically this can be done by ultrasound pulse reflection or by timeof flight (TOF) measurements of photons, where the time between a laserpulse emission and reception is measured. In both methods the materialsurrounding the canal entrance 214 reflects the waves sent from the handpiece 212 to the object containing the canal 216. As meanwhileinexpensive integrated circuits with mechanical dimensions in the orderof few mm are available offering optical distance measurement based onTOF (e.g. STM VL53L0x, VL6180x), such a chip 220 can be integrated in afront section 222 of the applicator hand piece 212.

The measurements range is specified from 0 cm to around 200 cm, whilethe distance measurement from 0 to 5 cm is not very precise. To improvethis the distance can be virtually enlarged by adding optical fibers 224in front of the sensitive sections of the TOF-sensors 220 as SPADsensors and the light source, as shown in FIG. 14 . This givesadditional pathway length and thus shifts the distance into a bettermeasureable region. The fibers 224 should have a length of 2-8 cm. Tofurther improve the distance resolution two or more such chips can beused in combination with fibers of different length targeting on thesame region to create overlapping time bins.

One time bin of such ICs is typically 50 ps. Therefore time delaydifferences created with optical fibers as delay lines of e.g. 25 ps incase of two chips or 16 ps and 32 ps in case of 3 chips will improve thedistance resolution by enabling to interpolate between the differenttime bins.

One of the available ICs offers already an integrated solution combiningthe TOF distance measurement with detection of ambient light.Differently to the ambient light detection method described elsewhere inthe text the ambient light is not collected via the fiber tip 218delivering the laser radiation, but at the distal end 210 of applicatorhand piece 212, with a detection direction “looking” slightly from theside towards the fiber tip 218 without having the fiber tip 218 directedin the aperture 226 of the TOF sensor optics 228.

For hygienic reasons such a hand piece 212 is typically built with acentral not sterilizable part 230 containing optics and electronics andan outer envelope 232 as shell or housing which is sterilizable. Thisshell must have additional optical windows 234 to allow the measurementradiation pass through the shell. (See FIG. 13 )

This measurement methods can be combined with all other“in-canal-detection” methods described in the application. Recording thedata of one or several “fiber-in-canal” detection methods over timeallows to define a typical time profile of a normal use of the device,as show in FIGS. 15 and 16 . Abnormal time profiles may be used todetect an abuse of the device and the laser may not be switched on or isswitched off when already active. (See FIG. 17 )

FIG. 13 shows a sketch of the laser hand piece 212 with the outerremovable and sterilizable shell 232 and the inner part 230 with opticaland electronic components as a laser delivery fiber 236, the focusinglens 238, the deflection mirror 240 and the Time of flight measurementcomponents comprising the TOF chip 220, two optical fibers as delaylines 224, the sensor optics 228 with deflection 242 and focusingelement 244. The optical fiber tip 218 is plugged into the hand piece212.

The Deflection and focusing element 228 is targeting the TOF laser beamand corresponding light path backwards to the receiver section of thechip 220 towards the vicinity of the distal end of the fiber tip 218.

In case of using a fluid spray (not shown in FIG. 13 ) the fluid spraycan be switched off periodically to avoid disturbance of themeasurement.

FIG. 14 shows details of distance measurement components. The TOF chip220 has two apertures for the emitter 246 and receiver 248. Bothapertures are coupled with focusing elements 249 into optical fibers 224and distal of the fibers 224 the light from light emitter and to thelight receiver are coupled via the focusing element 244 into thedeflection optics 242 (prism, mirror). In case the TOF chip providesadditional ambient light measurement via a third aperture, a third fiberwith same coupling is used.

FIG. 15 shows course of times or time profiles 250, 252, 254, 256, 258of the different “fiber in canal” detection measurements.

First time profile 250 shows the TOF measurement. Most important is thecriterion of the distance D between the focusing element 238 and adistal end 260 of the fiber tip 218 smaller than the length L of thefiber tip 218 corresponding in the time profile 250 to line 262 at 3 cm,which indicates the fiber 218 must be in the canal 216 of an object.

Additionally the ambient light measurement of the TOF chip 220 detectsan increase of the ambient light when approaching the extra-oral area ofthe patient because the treatment unit light is reflected from thepatient's skin and from the teeth when coming closer (second diagram252).

In the third diagram 254 the ambient light measurement through the fibertip 218 is most significant at the moment the fiber tip 218 isintroduced in the “dark” canal 216, where no ambient light is available.

When using light reflection measurement through the fiber tip 218, thereflection will increase when approaching the tooth and be maximal whenworking in the canal 216 (fourth diagram 256).

Finally in the impedance measurement diagram (fifth diagram 258) mostimportant is the point in time t5, where the metallic coating of thefiber tip immerses into the canal filled with conductive fluid, when theimpedance lowers from close to indefinite to laser radiation a muchsmaller value.

In case of non-medical applications using the diagrams 264, 266, 268,270, 272 are seen in FIG. 16 . Non-medical applications are for exampleworking channels of endoscopes or channels or tubes of bioreactors.Again in the first diagram the 264 TOF measurement is most significantat time t3 to t6, when the measured distance is smaller than the lengthof the fiber tip (time 274 at 10 cm in the example) because the tip mustbe in a canal of object.

Ambient light measured with the ambient light detector integrated in theTOF chip will increase when coming closer to the object, but can getlower when coming even closer to the object due to shading the ambientlight with the hand piece (second diagram 266).

Ambient light measurement through the fiber tip shows a significantdecrease at time t3, when entering into the canal with the fiber tip, atleast in objects which are no translucent for ambient light (thirddiagram 268).

The reflected light measurement in the fourth diagram 270 will showincreasing reflection at time t3 when approaching the object and bemaximal when the fiber tip is in the canal (time t3 to t6) of a highlyscattering, low absorbance object (fourth diagram 270).

Finally the impedance measurement shows a significant drop of impedanceat time t3 when immersing the metal coated surface of the fiber tip inthe canal filled with cleaning fluid (fifth diagram 272).

FIG. 17 shows time profiles or course of time 276, 278, 280, 282, 284 ofabusing the device by approaching the eye of a person for example incase of a medical/dental application. In that case the distancemeasurement will never be smaller than the fiber tip length (time 286 infirst diagram 276), the ambient light will increase (second diagram 278)and the ambient light measurement through the fiber tip will not drop(third diagram 280) and impedance measurement will not show a decreasingimpedance as long the eye is not touched directly with tip (fifthdiagram 284).

Another method to detect the fiber tip 18 position inside a root canal10 is to metallize the surface of the fiber 14, inject a measurementcurrent (AC) into the electrode(s) 180, 182 and measure the impedancechange during insertion of the fiber into the root canal 10. The fiber14 may be fully metallized as one electrode in combination with acounter electrode held by the patient or attached to the mouth of thepatient (lip clip). A preferred solution is, however, a dual electrodeconcept, i.e. a first and a second electrode 180, 182, avoiding acounter electrode. Unambiguous connection is guaranteed by indexing thefiber tip.

Metallization layer may consist of a full coating of the optical fiberexcept the conical part of the fiber tip or may be a structured layerforming one or more electrodes on the same outer fiber surface.

A metallized tip configuration enables further “Canal is still wet”detection preferably with a dual electrode metallized fiber tip (seeFIG. 5 ).

A wet canal has a significantly higher relative permittivity constantcompared to a dry canal. H₂O: {grave over (ε)}: 80-90 and ε̋: 3-30compared to dentin {grave over (ε)}: 1-8 and ε̋: 0.3-5. This can beutilized to determine the degree of humidity of the root canal.Measurement is done with a single frequency or multiple singlefrequencies or a sweep over a frequency band, which can be in the range1 Hz to 10 GHz, preferably 1 kHz-2.4 GHz. A hydrophobic coating isapplied in the area of the electrode to avoid direct not reversiblewetting of the electrodes.

Using the canal humidity detection in combination with a laser basedcanal drying procedure, by applying laser energy with 0.1-1 W with200-800 Hz pulse repetition rate allows a feedback controlled canaldrying procedure.

Further impedance spectroscopy can be used for bacteria detection in theroot canal 10 and length measurement during cleaning the canal 10. Aspecial variant of impedance spectroscopy offered by NuMed (U.S. Pat.No. 9,119,548B2) analyzing the harmonics generated by bacteria cellwalls, can be integrated into the proposed cleaning device and allowbacteria detection in the root canal.

Using the metallized fiber 14, root canal length measurement withimpedance measurements can be performed simultaneously with cleaning toindicate the correct position of the fiber tip 18 during treatment andnot to exceed the apex 20.

To differentiate an upper jaw from a lower jaw treatment an inertialsensor e.g. is used (MEMs device e.g. Kionix KXTF9). This is important,since the fluid refill rate is different treating upper or lower jawcases.

Further this inertial platform provides data for the movement directionof the fiber tip 18 (into- or out of the root canal 10). This isimportant to switch off the laser when pushing the fiber tip 18 into theroot canal 10, in case an application requires an energy density abovethe ablation threshold.

Further the motion information provided by the motion sensor can be usedto detect whether the dentist is continuously moving the fiber in thecanal and remind the dentist with warning information, if he stops themovement during treatment and reduce or switch off the laser power.

Additionally the inertial platform data can be used to crosscheck withthe fiber position data provided from the impedance based fiber positionmeasurement.

The delivery system 50 connects the portable desktop device 40 with thehandpiece 48 similar to a dental drill handpiece.

To avoid torque on the light guide the handpiece 48 is connected to thedelivery system 50 with free rotation with low friction around thelongitudinal axis.

The laser radiation is transported via a GeO, sapphire, ZrF₄ or anyother light guide capable transmitting radiation (up to 50 mJ, up to 5 WAvg. power, 500 W peak power) in the wavelength range 2.69-2.94 μm andadditionally 400 nm-1000 nm to the handpiece. The core diameter of thelight guide fiber is between 150 and 600 μm, preferably 180-250 μm. Thelight guide end surfaces are protected against moisture and may becoated with an anti-reflective material.

Compressed air and water available at the dental unit of the dentalchair, connected to the device is guided through the delivery systemtogether with the light guide.

Optional further cleaning fluids from exchangeable containers plugged inthe device can be transported in the delivery system to the handpiece.

Electrical wires provide data and power transport between handpiece anddesktop unit. To keep the number of wires and connectors low, a SPI- orI²C-bus system is used.

A bending protection insures that the fiber 14 is not bended beyond theallowed bending radius for oscillating bending.

The delivery system 50 is detachable from device in case of a need forrepair and the handpiece 48 can be detached from the delivery system 50routinely for cleaning/sterilization.

FIG. 7 is a schematic depiction of the delivery system 50 which isself-explaining.

As an alternative to the placement of the motion sensor in the handpiecethe sensor can be placed in the most distal part of the delivery system.This would avoid sterilization cycles to be applied to the sensor chip.Then however a rotation position detection between handpiece anddelivery system must be added.

The handpiece 48 is connected with the delivery system 50 with arotational coupling 58, which allows to deliver water (line 60) andpressurized air (line 62) to the handpiece 48. Air and water aredelivered to the front section of the handpiece 48 and are appliedtowards the fiber 14 with nozzles 64. The laser radiation is suppliedfrom the delivery system 50 with an optical fiber 66, via a protectionwindow 68, a lens 70, and a deflection mirror 72 to the fiber 14. Fluidcontainers 54 are snapped on the handpiece 48. A motion sensor 74 isplaced in the front section of the delivery system 50 and can detect incombination with a rotation encoder 76 the motion of the fiber tip 18(see also FIG. 8 ).

In the handheld applicator a removable, disposable fiber 14 can beplugged in under an angle in the order 70-130° to main direction of thehandpiece 48. This fiber tip 18 is introduced into the root canal.

The handpiece 48 is comparable to a small dental handpiece, ideallycontra-angle. The handpiece 48 is rotatable around longitudinal axis.

The laser beam deflection into attachable fiber 14 by ˜90° is performedwith the flat mirror 72 and a separate focusing element or a focusingmirror.

The disposable fiber 14 is connected to the handpiece 48 with aconnector allowing unique positioning with an indexing connection toallow at least 2 electrical connections unambiguously being connected tocontacts in the handpiece 48.

In a simple version of the handpiece 48 only water and air are availablefor the treatment directly out of the handpiece 48. Other cleaningfluids are applied manually with a syringe into the root canals 10.

Pressurized air and water may form a mist. 10-30 ml/min water and 5-10l/min air are used to form the mist.

A fluid beam is directed towards the last ⅓ of fiber 14 with angle ca.10-20° from fiber 14 longitudinal axis. The water speed at exit of thehandpiece is larger than 0.6 m/s.

A Start/Stop button may be integrated in the handpiece.

A schematic depiction of the handpiece 48 with its components is shownin FIG. 9 , which is self-explaining.

In a variant of the handpiece 48 disposable fluid containers 54/(alsocalled cartridges) for NaOCl and EDTA are directly attached toapplicator. The cartridge 54 has a fluid guidance close to the fiber 14(see FIG. 10 ). A direct placement at the handpiece 48 is possible sincethe treatment requires only small amounts of fluid in the order of 1-2ml per fluid. Main objective is to keep the partially corrosive fluidsseparate from the handpiece 48, delivery system 50 and desktop device40. Further objective is to avoid dripping before and after usage. Aninexpensive solution to achieve these objectives is the separation of anelectromagnetic valve 78 into the excitation part with the magnetic coil80 and a part of the ferromagnetic core 82 in the handpiece 48 and aferromagnetic material as valve 78 opener as part of the exit valve inthe disposable cartridge 54. The cartridge 54 is set under air pressurewhen placing the cartridge 54 in the handpiece 48. A flexible membraneor a piston 84 may separate the fluid from the air inlet. For moredetails, see FIG. 11 .

In a further variant of the device the device is not connected to thedental treatment center. To get the device completely independent of thesupply with fluid and air from a dental treatment center a detachablefluid container can be placed on the laser device (not on the hand pieceas proposed for the cleaning fluids as described before).

As an air compressor inside the laser device to pressurize the system isnoisy a detachable fluid container is used, which is pre-pressurizedcomparable to a spray can. The connection to the fluid delivery systeminside the laser device is done by a cylinder entering into an O-ring tofirst create a pressure dense seal and then open the pathway from thecontainer to the fluid supply system. The container is partially filledwith fluid 10 ml-1 l, most preferable 100 ml-250 ml. The rest of thecontainer is space for the gas providing the pressure. The gas may beair, inert gas.

As an alternative a substance with a vapor pressure around 3-8 bar atroom temperature e.g. Butane in combination with partitioning the insideof the fluid container into two compartments, separated by flexiblemembrane.

The fluid in the container can be sterilized water, physiological salinesolution or other fluids, optionally containing bactericidal ingredientsas e.g. H₂O₂ or CHX, but not limited to.

To keep the internal tubing and valves free of biofilm a secondcontainer with a sterilization fluid can be attached instead of thecleaning fluid for daily/weekly cleaning as known from dental treatmentcenters.

To prohibit the intended use of the system as long sterilization fluidis in the system, the sterilization fluid container has means foridentification e.g. RF ID chip or a mechanical marker to inform thelaser device that it cannot be used for canal cleaning. After removal ofthe sterilization fluid container the software of the sterilizationcontrol requests first a normal cleaning fluid container to be attachedand then enough fluid is released into the tubing system to completelyreplace the sterilization fluid. After completing the sterilizationprocedure the device can be used for canal cleaning or can be stored.

Another option is to place the sterilization fluid container additionalas a second one on laser device parallel to the cleaning fluidcontainer.

In case no connection to a dental treatment center (dental chair) isdesired and using cleaning fluid cartridges mounted on the hand piece,the second container can be just filled with pressurized gas to supportthe pressurization of the cartridges on the hand piece.

As the laser device is in this option not connected to a dentaltreatment center (dental chair) no pressurized air is available. In thiscase the water mist is generated by water only in combination with aspecial nozzle.

FIG. 18 shows the positioning of a fluid container 300 on a laser device302 in form of a table top device having a handpiece 212. The fluidcontainer 300 is screwed top down into the laser device 302, enablingthe fluid to be pressed out of the container 300 into the tubing of thelaser device 302 only after a fluid and air tight connection isestablished between the fluid container 300 and the laser device 302.The connection is reversible. If there should be a rest of fluid andpressure still in the container 300 when it is removed, no fluid or gaswill exit the container 300 The proposed solution is not limited to onefluid container. There may be a separate container with disinfectionfluid be placed in the same way in the laser device for biofilm removalparallel to the cleaning fluid container, to avoid the exchange of thecontainer for the daily/weekly disinfection procedure of the device.

FIG. 19 shows details of fluid container 300 with the cleaning fluid 304and the pressurized gas reservoir 306. A valve mechanism 308 placed in acontainer cap 310 which allows water flow only after a water and gastight connection has been established between the container and thetubing of the laser device. The corresponding part in the laser deviceis a tube 312 with an O-ring 314, which establishes the air and gastight connection to the container. A screw thread on the container topfixes the container to the laser device.

The container can be made of metal or reinforced plastic sustainingpressure in the range of 3-10 bar. Water mist is generated emanatingfrom the laser device in form of a handpiece via an airless workingnozzle.

The fiber material must allow the transmission of a wavelength rangefrom 400 nm to 2.94 μm with reasonable loss and cost. OH reduced silicafibers are an acceptable compromise with ˜50% attenuation over 5 cmlength at 2.94 μm (including Fresnel reflection). The fiber 14 is adisposable surviving 3-4 root canals with moderate degradation. The end18 of the fiber 14 is conically shaped without protection layer ormetallization. Alternatively the fiber 14 can be hemispherical. Thefiber 14 has an outer diameter of 200-300 μm and a core diameter of180-240 μm. The length of the fiber 14 is between 30-40 mm. A moldedplastic part connects the fiber 14 with the handpiece. The fiber 14 mayhave an additional coating to improve fracture resistance and may have asurface metallization to allow measuring the insertion length in theroot canal, to determine the distance to the apex during treatment. Thecontact surfaces of the electrodes contact to connectors in the couplingto the handpiece 48. The coupling part to the handpieces 48 allows only2 180° rotated positions to allow for unambiguous connection of the twoelectrodes. The electrodes 180, 182 may be covered with a hydrophobiclayer. Further details of the fiber 14 with its tip can be learned fromFIG. 12 .

A software controls the laser parameters, air and water flow and in theextended handpiece 48 variant the flow of up to two additional cleaningfluids.

Sequencer programs are available for the following applications:

-   -   Cleaning/Drying    -   Bacteria detection    -   Thermal bacteria reduction    -   aPDT    -   Apical plug placement    -   Obturation support

The Cleaning/drying program provides a sequence of cleaning and dryingsteps (see TABLE II). The parameters can be program individually andstored as “Preferred treatment programs”.

Bacteria detection is a program to detect remaining bacteria and/orbacteria residuals in the root canal via fluorescence detection.

Thermal bacteria reduction is a program to heat the inner root canalsurface locally in a clear defined way. Pulse repetition ratespreferably between 100 and 2000 Hz are used in combination with lowpulse energies (0.1-1 mJ) to generate locally temperatures on the innerroot surface and within a few 100^(th) of μm in the root canal wall highenough to kill remaining bacteria. No fluids are used in this program.Fiber motion is monitored by the motion detector to avoid any risk oflocal over-heating.

The aPDT program combines the traditional aPDT sequence known e.g. fromHelbo with the laser generated steam bubbles to create motion in theaPDT dye fluid to enhance the contact and fluid exchange along the rootcanal wall. Instead of a cleaning fluid container an aPDT dye isinserted in the handpiece. After the aPDT the Dye is washed out the rootcanal automatically by flushing with water with support of lasergenerated steam bubbles.

For an irregular, not shaped root canal 10 a different obturationstrategy is required. To support such an obturation method the deviceoffers the following programs:

The apical plug placement program is used in combination with a fiberwith attached gutta-percha plug. With the laser heat is applied topartially melt the plug in apical position and detach it from the fibertip.

The obturation support program is used to accelerate a low viscosityobturation material placed over the apical plug in the root canalagainst the root canal wall to enhance the dense coverage of the wholeroot canal wall with obturation material. For that purpose transientsteam bubbles are generated in the root canal filling material. Theapplied heat can further reduce the viscosity during the applicationadditionally enabling the obturation material to creep in any niche ofthe canal.

The invention provides an automated control of the laser parameters andthe sequencing of the cleaning fluids, laser assisted drying andcompressed air, which allows a fully automated cleaning process.

Although the invention has been explained above with the help of thecleaning of a root canal, the teaching according to the invention is, aswas already explained, suitable for the cleaning of canals in whichcanals of smaller diameters as those of root canals are to be cleaned,particularly such canals which do not extend evenly in theirlongitudinal direction. With respect to this, reference is made to theintroductory explanations.

The invention claimed is:
 1. A method for the cleaning of acircumferentially closed canal by means of a light guide conducting alaser beam, comprising: measuring a position of a free end of the lightguide within the canal; wherein a supply of the laser beam to the lightguide is interrupted when the free end of the light guide is moved frominside the canal to outside the canal; monitoring a movement of thelight guide within the canal; turning off or reducing an output of alaser radiation, responsive to detecting that there is no movement orthe movement is below a first threshold value, based on at least onesignal change representative of the movement, wherein a verification ofwhether the light guide is inside the canal or outside the canal iscarried out through a combination of: a) radiation received by the lightguide that is derived from an area surrounding the light guide, b)through a changing reflection component of a radiation reflected at thefree end of the light guide, c) measurement of a change in impedance viaan outer metallization of the light guide, d) measuring the distance tothe nearest object in the vicinity of a fiber tip with time of flightmeasurement (TOF), e) measuring the ambient light with a sensorintegrated in a TOF chip, and f) measuring the distance to the nearestobject in the vicinity of the fiber tip by ultrasound pulses and whereinthe combination is a combination selected from the group consisting ofa)+b), a)+c), b)+c), c)+f), a)+b)+c), c)+d), d)+e), and c)+d)+e),wherein data of one or several verification methods that detect theentry of the light guide in the canal is recorded over a plurality oftime intervals corresponding to a plurality of usages of the light guideand said data is stored to obtain a plurality of time profiles thatdefine at least a normal use and an abnormal use of the light guide,said normal use comprising entering the canal with a fiber of the lightguide, moving the fiber up and down the canal and removing the fiberfrom the canal, and said abnormal use comprising moving the fiber tiptowards an eye and, wherein responsive to obtaining said plurality oftime profiles, detecting the abnormal use based on the plurality of timeprofiles, and either prohibiting switching the laser on or switching thelaser off responsive to said laser being already active.
 2. A methodaccording to claim 1, wherein the turning off of the laser radiation orits reducing is controlled in dependency of at least two signal changesand/or two second thresholds different from each other and/or signalchanges relative to the two second thresholds determined during at leasttwo courses of time determined in dependency of the entry of the lightguide into the canal.
 3. A method according to claim 1, wherein materialpresent on the inside of the canal is removed through laser-inducedhydrodynamic fluid movement.
 4. A method according to claim 1, furthercomprising enhancing bacteria killing with traditional PDT (photodynamictherapy) fluids by using laser induced hydrodynamic fluid motion toagitate these fluids.